This invention relates to a method for the drilling and completion of oil wells of small intermediate diameter for application in ultra deep water.
One of the major problems currently faced by operation and oil production in deep water is that of finding drilling and completion rigs on the market at an accessible cost.
The development of operations in deep waters has experienced a growing impetus with new technologies which reduce design time and cut costs. Thus for wells in deep water the time from discovery to the start of production is gradually falling, as is the appraisal work. The normal period between discovery and first production is continually tending to decrease.
The decision to operate in deep water restricts the availability of specialist equipment, particularly drilling rigs, increasing the development cost. Thus the contracting of vessels for deep water work has proved to be quite difficult because of their scarcity on the market, which results in an increase in the cost of chartering these vessels.
The availability of rigs at accessible prices for carrying out oil drilling and completion operations in deep waters is essential if oil production is to be increased.
As one way of making such equipment available, there is the option of modifying existing vessels for operations involving deeper wells. Nevertheless, because of the increase in load resulting from the greater length of riser which is needed to reach greater depths, this task involves the need to make a considerable increase in the available space on the vessels and to increase their buoyancy.
At the present time the risers used in oil exploration and drilling are 21 inches (53.34 cm) in outside diameter. Wells are typically drilled in five stages, each characterized by drilling with a particular diameter. During the first stage the tools used permit the use of 30 inch (76.20 cm) outside diameter casing. Casing of 20 inches (53.34 cm) outside diameter is used in the second stage. Casing of 13xe2x85x9c inches (33.97 cm) outside diameter is used in the third stage. The fourth stage uses 9⅝ inch (24.45 cm)outside diameter casing. Finally, the fifth stage uses a suspended pipe, known by specialists as a liner, of 7 inches outside diameter (17.78 cm), supported by the casing of immediately greater diameter.
It should be emphasized that the casings extend from the wellhead to the ends of the stages drilled to their specific diameters. The liner is a pipe placed in the well and of limited length sufficient to occupy only a particular part of the well, which has been drilled to its diameter and which extends from its lowest point within the well to a point located at a particular depth below the wellhead. In other words, the liner does not occupy the entire length of the well, but only part of it.
This invention aims to propose a method which overcomes the problems mentioned above.
It is another object of this invention to establish a method whose use will reduce the cost of drilling and operating oil wells drilled in ultra deep water. This cost reduction is brought about by reducing the intermediate diameters of pipes used in the various stages of well drilling, and also by reducing the weight of the rising tubing used in drilling operations, known by those skilled in the art as the xe2x80x9criserxe2x80x9d, which makes it possible for vessels currently used in shallower waters to operate in deeper waters.
This invention provides a method for drilling and completing an oil well of small intermediate diameter in ultra deep water that comprises a first stage of drilling and running at least two casings and then a second stage of drilling and running at least two suspended liners, in which a first liner is fixed to a lower end of a last run casing of immediately greater diameter and the second and any subsequent liners are successively fixed to a lower end of a respective previously run liner of immediately larger diameter.
In a preferred embodiment of the method according to this invention includes: a first stage incorporates the phases of:
drilling and running a first casing, and
drilling and running a second casing,
and a second stage with the phases of:
drilling and running a first liner,
drilling and running a second liner,
drilling and running a third liner.
This method provides the opportunity for a significant reduction in well drilling costs, in respect of both the material used in drilling and completion, and materials used in support equipment for drilling operations.